Various types of driving arrangements are known for pumps and compressors. The type is typically chosen on basis of parameters as weight, volume, force, speed, sound level, vibration level, reliability, available power supply, and price, etc. For instance, for subsea applications one particularly wants a reliable driving arrangement which requires less maintenance and which can be driven with hydraulics or electrical power.
From patent publication U.S. Pat. No. 7,287,595 it is known to use an electric motor to drive a hydraulic piston for supplying hydraulic pressure in a subsea environment. The electric engine is connected to a roller screw assembly (170) through a planet gear (190). To the roller screw is connected a piston stem (134) which in its opposite end is fixed to a hydraulic piston (130). The assembly can thus provide a hydraulic pressure by means of electric power to the electric motor, which hydraulic pressure is accumulated in an accumulator (142). In this way one avoids that hydraulic umbilicals must be guided from the sea surface, down to a subsea well, for instance.
In the solution shown in U.S. Pat. No. 7,287,595, it is worth noting that the stroke length of the piston stem (134) is limited to the area between the planet gear (190) and the outer (lowermost) limit for movement in the roller screw assembly (170).
Patent publication U.S. Pat. No. 4,145,165 describes a long stroke pump which has a threaded rod which extends through the rotor of an electric motor. When running the rotor, the rod will move axially in a reciprocating path due to the threaded engagement with the rotor. The two ends of the rod function as two plungers which provide pumping action by repeatedly entering and leaving two adjacent chambers.
In addition, patent application publication US 2009/0053074, which was published on 26 Feb. 2009, describes a similar displacement pump which uses an electric linear motor for providing a similar reciprocating movement of a piston rod. This pump uses pistons at respective ends of a piston rod.
Furthermore it is known to provide the piston movement by attaching the piston stem, directly or indirectly, to a crankshaft (see FIG. 1) or a flywheel. Such a crankshaft or flywheel will have an axial direction crosswise to the stroke length of the piston. This makes the assembly space demanding. Furthermore the stroke length is limited by the dimensions of the crankshaft or flywheel in the radial direction.
It is a purpose of the present invention to provide a driving arrangement for pumps and compressors which avoids the disadvantages mentioned above, and which in addition exhibits additional advantages in respect to the prior art.